An anaerobic hardening composition is one which does not harden and is generally stable for a long period of time when in contact with air or oxygen, but which is polymerized to harden in the absence of air or oxygen, for example, when situated between two adjacent faces from which air or oxygen has been shielded. The composition is used for adhesion, sealing or fixation of metal parts and the like.
Anaerobic hardening compositions comprising a monomer component consisting essentially of an acrylate monomer and/or a methacrylate monomer and an organic peroxide as a polymerization initiator are known. However the known anaerobic hardening composition has a drawback in that the adhesion power of the hardened product noticeably lowers under a high temperature condition. Specifically, after the composition has been anaerobically polymerized and hardened in use for adhesion, sealing and fixation, the adhesive power of the hardened product noticeably lowers when the product is under a high temperature condition.
On the other hand, silicone products made from polyorganosiloxanes are used in various fields since they have excellent heat resistance, cold resistance and chemical resistance. It is extremely difficult to impart a so-called anaerobic hardening property to such polyorganosiloxanes. Hitherto, there is known a composition comprising an acryl and/or methacryl group-containing polyorganosiloxane and a hydroperoxide as a polymerization initiator (refer to Japanese Patent Application Laid-Open No. 53-142493) and a composition consisting essentially of a linear polyorganosiloxane which has (an) acryloyl and/or methacryloyl group(s) and a hydrolyzable group at both ends of the molecular chain (refer to Japanese Patent Application Laid-Open No. 1-287115). However, these compositions have a serious problem in that their hardening speed and adhesiveness-revealing speed are extremely low.